Benzene hexachloride production



United States PatentOfiice 2,758,077 Patented Aug. 7, 1956 December 7, 1954. Divided and this application December 6, 1954, Serial No. 480,601

(Filed under Rule 47(a) and 35 U. S. C. 116) '1 Claim. (Cl. 204-163) This invention relates to a new process for producing benzene hexachloride products unusually rich in the gamma isomeric form of this compound, and the products thus produced. This application is a division of our prior application Serial No. 695,276, U. S. 2,696,509, filed September 6, 1946. This case is also related to'ou'r co pending application Serial No. 480,602 filed the same day as this application.

Benzene hexachloride (this term is used throughout the specification and claim to indicate any one'of the isomeric forms of 1,2,3,4,5,6-hexachlorocyclohexane, as well as mixtures of the isomers of this compound) is made by addition of three molecules of chlorine to one of. benzene. The resulting compound contains one chlo-' rine atom on each carbon atom of the benzene. benzene hexachloride product that is formed when chlorine is reacted with benzene has long been considered to be a mixture of stereoisomeric forms, the so called alpha, beta, gamma, and delta forms having been recognized; these are stated to be present in the approximately fixed proportion of 70% of the 'alpha'isomer, of the beta isomer, to 12% of the gamma isomer, and 13 to 15% of the delta isomer.

It is known in the art that this customary mixture of the benzene hexachloride isomers has insecticidal value; but that it is in only one of the isomeric forms of hen-- zene hexachloride, namely the gamma form, that sub stantially all this insecticidal value resides. Even though benzene hexachloride is greatly diluted when it is compounded into insecticides, the presence of large amounts of insecticidally inactive organic materials such as the alpha and beta isomers is considered undesirable by the compounder of insecticides. Ideally, therefore, a benzene hexachloride product for compounding into insecticides should consist solely or'largely of the gamma isomer. 1

-However, it has not heretofore been commercially feasible to produce a benzene hexachloride material for insecticidal purposes containing appreciably morethan the natural proportion of 10 to 12% gamma isomer, since the separation of even a gamma-rich product from the'natural mixture of four isomers has involved the te.- dious and costly steps of successive resolutions and which has formed, and (d) separately recovering, without further chlorination, benzene hexachloride product of reaction that remains in solution in 'the liquid phase material separated in the preceding step. We have found it desirable 'to correlate the temperature of the separation step (c)' with the extent of chlorination; thus when chlorination doesnot go beyond the preferred limit of about 50% of the total reaction mixture, the separation step (c) is carried out at a temperature not higher than about 40C., whereas when the extent of chlorination goes beyond about 50%, the separation step (c) is preferably carried out at a somewhat warmer temperature, say 40 to 80 C., and when the extent of chlorination does not exceed about 40%, the separation step may advantageously be carried out at about 25 C. 'Although it is convenient to use chlorine in gaseous form in our process, other forms, e. g., liquid chlorine, may be used.

We have found that by following the steps above outlined, the benzene hexachloride product obtained in step (of) above exhibits from '3 to 7 times the insecticidal v efiicacy of the products which have heretofore been recovered directly from the chlorination reaction'mixture.

The

For example, the gamma isomer concentration in the product prepared according to our invention is usually at least 20 to 30%, and may be as high as 90% or more, whereas the gamma isomer concentration in products prepared by comparable prior art processes'is usually in the range of 10 to 12%. We have further found that our gamma isomer rich benzene hexachloride product is substantially free from higher chlorinated prod-' ucts, such as' the heptachloro derivative of benzene,

' which might have a deleterious efiect on the compounding of our product for the various applications herein after described. e r

In a preferred method of carrying out the process of our invention, gaseous chlorine is led into a solution of benzene in carbon tetrachloride, the carbon tetrachlocrystallizations, whereby a gamma-rich product may: I

products.

We have now discovered a process for chlorination of benzene and the recovery of the benzene hexachloride formed, whereby a gamma-rich benzene hexachloride product may be obtained from the synthesis reaction mixture. Our process involves the successive stepsof (a) chlorinating benzene in a solution of benzene in carbon tetrachloride,-while exposing to actinic light, whereby benzene is converted to benzene hexachloride, (b) discontinuing such chlorination when the total quantity of benzene converted to benzene hexachloride amounts to from about 10% to preferably from about 25% to 50%, of the total quantity-of liquid reaction mixture, (0) separating the solid phase material ride being substantially inert under the conditions of use; the said solution preferably containing only a minor proportion by volume of benzene. The chlorination is carried out in the presence of actinic irradiation, e. g. the irradiation emitted by an ultra-violet lamp, bright sunlight, or other source of actinic light. The introduc' tion of chlorine is preferably carried out with cooling if necessary to maintain the mixture below about 40 to 50 C. It is important that the chlorination step be carried out in the absence of metal catalysts which produce substitution reactions, since such products are undesired impurities and decrease the yield of benzene hexachloride. Under these conditions benzene hexachloride is substantially the only chlorination product formed from the benzene. Chlorination is discontinued before the quantity of benzene chlorinated amounts to more than about one-half of the total liquid reaction mixture; on a liquid volume basis. In the case wherethe solution of benzene and carbon tetrachloride contains no more than a minor proportion by volume of benzene, the benzenepresent may of course be completely chlorinated limitation on the extent of chlorination.

Agitation of the reaction mixture is preferably main tained during chlorination and, after chlorination has been discontinued, the mixture is preferably further agitatedand treated to eliminate unreacted chlorine. The chlorine-free reaction mixture is then cooled and maintained at a temperature not higher than about 40. C.,

preferablyat room temperature or slightly below, while the solid phase which is formed is separated, e. g. by filtration. The separated solid represents thepart of :the benzene hexachloride product of chlorination that is richer in alpha and beta isomers than the whole product normally formed upon chlorination... Under. the condi- I alpha and beta'concentrate.

tions described, from 50 to 75% of the whole benzene hexachloride reaction product'mayjthus precipitate as lThe solution, remaining-after removal of the solid alpha 7 I "and beta isomers, contains dissolved therein, substantially all of the gamma isomer formed during-chlorination.

compounded into all the customary types of insecticidal compositions. Thus, the liquid may be adsorbed on'or I I absorbed in a coniminuted solid carrier material such as pyrophyllite, ,or a clay, with milling, in suitably small proportions for insecticidal purposes, and the resulting, I I

I pl'GdllClGiS anressentially dry,free fiowing powder. To

This solution is-now treated to recover this product, here inafte'r referred to as gamma-rich remaindenprocluctfi The gamma-rich remainder product may be recovered by evaporation, of the volatile solvent and anYgimreac'ted benzene.

The gamma-rich remainder product thus recovered is then preferably further processed to obtain it in .a more desirable form. This may beldoneby chilling, preferably at.a temperaturesof ,0 .to; 5 (2., .tocrystallizeit ,atleast inpart. :The crystallized. gamma concentrate maythen beseparatedfrom the. residualroil (if thereisany), e. g.

by, centrifuging. -I-f a .water or alkalinewashhas been I employed, these; products may be dried, .thegsolid (hereinafter. called solid. gamma= concentrate?) by lair drying and the liquidg(hereinafter called residual oil?) by a solid .dehydratingagent suchvasscalciurn sulfate. I

i -AlL of the above, products, i.,e. the gamma-rich re mainde'r'pro cluct, as swellsas the solid gamma. concen- The gamma-rich remainder product which, upon? chil- "1.45-2001C. 'After'the sixthhour of chlorination, .=99.4

lingand standing separates into twophases, solid gamma,

concentrateandresidual oil, mayitself beslookedvupon asqan end product, :as abovesuggested, since, it may ;be

employed directly in insecticide formulation. This, prod uctnmay be characterized by the following properties:

Content on all benzene 'hexachloride isomers, at least I 12 hours below about 5, C. I Percent insecticidal effectiveness, as compared to pure gamma isomer to 90%, more usually to'60%.

The above-described solid gamma concentrate of our inventionis characterized by the following properties:

:The residual oil-of, our invention-is characterized'by the following properties:

Content-of all b'enzene hexachloride isomers, at-least Boilingrange at 3 mm.Hg 90% over within 120*t0' Percent-insecticidal effectiveness, as compared to pure gamma isomer 20 to90%, more usually'25 to 50%.

.Any ofthe above products when solid, may be compounded intodusts, sprays,emulsions, and other insecticidal compositions in the usual manner, e. g. maylbc compounded into an insecticidal dust by milling. together in desired proportions a mixture of a smallamount of the..crystal-product,-or a concentrated solution .thereof in acetone, and a carrier such as finely'divided pyrophyllite, ;or afinely divided clay; may zbermade; intota spray by dissolving a small'amount of the crystalproduct in a solvent suchas .xylene,ztoluene, ora 'methyl1 naphthaleneyor maybe madeinto an emulsion by dispersing: a. concentratedxylene solutionuof. the crystal. product in: water with a suitable emulsifying agentsu'ch .as. an alkylphenoxy polyethoxy' ethanol.

. Any of the above products, when liquid, =may;.also the From125 t0.' 75% crystallizes upon holding for at least I i i 40 form sprays or emulsions the liquid may,of course, be dissolvedina solvent such-as'xyleneor toluene :justk-as I the crystalline material. I I

' The following example :is illustrative of the process of our invention:

I Example I I '156 parts by weight of 'ben' zeneandl733 partsby weight. of carbon tetrachloride were charged into a reac 7 tion' vessel fitted with a stirrer, reflux condenser, chlorine inlet, external water spray. and a mercury vapor lamp for I supplying actiniclight to the mixture. chlorine-gaszwas passed in :with, agitation and irradiation, and. the reaction mixturecwascooled to 'maintainthe temperature below.40 C. After four hours ofchlorination, 206.2 parts ofsolids were removed by filtration having. a- ,rneltingvpointwof parts oftsolids having a melting point. oflZO-ZOO," .C.

were removed from the reaction mixture. .After. chlorinating for another'hour, no additional solids appeared to-be-comingout of solution and the chlorinationwas I discontinued, after which ;-10.5 parts of solids. having-a melting-point of: 180-200? C. were removed- The filtrate from the prior separation was evaporated on-asteam bath, 7 I 7 until all carbon tetrachloride was removed. The oil. that 'remained was 'chilled over a period of several hours and 2603 parts of gamma concentrate were obtained. Total conversion of the benzene tobenzene hexachloride was 99.3%." The gamma concentrate containing over 2.0%,

gamma isomer had a melting; point of 42-1 C.. and represented 44.8% of the. benzene converted to benzene hexachloride.

"Since many modifications are possible in the process and product of our invention as, above described without I departure from the scope of the invention, it is intended that-theebove description of'o'ur inventionshould be interpretedas illustrative, and the invention is not to be limitedexcept as set forth in the claim which follow.

We claim:

A process for production of a benzene hexachloride product rich in gamma isomer that comprises dissolving benzene in carbon tetrachloride to form a solution containing-no more than a minorproportion by volume of benzene,-reacting the benzene in said solution, with actinic light irradiation and agitation, with an amount of gaseous chlorine sufficient to convert substantially -all the benzene to benzene hexachloride, maintaining the temperature below about 40 C. during at least the greator part-of 'the chlorination step, removing solid phase material from the resulting chlorination reaction mixture while-maintaining the temperature below about 40 C. and-separatelyrecovering, without further chlorination, benzene'hexachloride product of reaction that remains in solution in the liquid phase material from the preceding step, chilling the latterbenzene hexachlorideproduct :to bring-about partial solidification thereof, and separating a solid phase product and a liquid phase product from the chilled-material.

- References Cited in the file of this patent UNITED STATES PATENTS 2,696,509 La Lande et al. "Dec. 7, 1954 FOREIGN PATENTS 573,693 'Great Britain Dec.'3, 1945 460,288 Belgium 'Oct. 31, 1945 OTHER REFERENCES Van-der Linden, Ber. der.Deutsche Chem. 'Gesellg". vol;45 ("1912) -,-:pp.*.23 1,23 6. 

